RFID tag ICs employ tunneling-voltage profile calibration during IC manufacturing to determine and store, typically in nonvolatile memory, a tunneling-voltage profile for writing data to the IC's nonvolatile memory. The IC may subsequently read the profile at power-up, prior to writing the memory, or at other times as determined by the IC or by an interrogating reader, and may determine an actual ramp profile for writing to the nonvolatile memory based on the read profile and one or more operating conditions. By using the read profile to determine an actual ramp profile for writing to the nonvolatile memory, the IC may reduce nonvolatile memory write time and oxide stress.